Environment-friendly cutting fluid and preparation method thereof

Abstract

An environment-friendly cutting fluid comprises, by weight percentage, 2-20% of long-chain dibasic acid-amino acid, 1-20% of amino acid long-chain alcohol ester, 1-20% of glycerol, 0.1-5% of sodium metasilicate and the balance of water, the long-chain dibasic acid-amino acid being obtained by connecting two amino acids to the carboxyl groups at both ends of the long-chain dibasic acid, and the amino acid long-chain alcohol ester being an alcohol ester compound formed by the reaction of amino acid and long-chain alcohol. The combination of the long-chain dibasic acid-amino acid and the amino acid long-chain alcohol ester makes the cutting fluid have strong lubricating performance and be applicable to the processing of aluminum alloy. The long-chain dibasic acid-amino acid and the sodium metasilicate have strong aluminum corrosion inhibition capacity, and their combination can protect the aluminum alloy during use.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of cutting fluid, in particular to an environment-friendly cutting fluid and a preparation method thereof. BACKGROUND

[0002] Aluminum alloy has the advantages of low density, high strength, good plasticity, good electrical conductivity, good thermal conductivity and good corrosion resistance, and is widely used in industry. As an indispensable process in the processing of aluminum alloy, a special aluminum alloy cutting fluid needs to be developed to meet its use requirements.

[0003] Aluminum alloy is soft and has good plasticity, and is prone to cause burr and form strip-shaped cracks during processing, thereby affecting the processing precision and surface roughness. Therefore, semi-synthetic cutting fluid is usually used to meet the lubrication performance required for processing. However, the mineral oil added in the semi-synthetic cutting fluid is prone to spoilage and poor in safety and environmental protection, and its future use will be strictly limited. The all-synthetic cutting fluid does not contain mineral oil, and is a more green and environmentally friendly cutting fluid type. However, the all-synthetic cutting fluid in the prior art has the problem of low lubrication performance, and is difficult to meet the processing requirements of aluminum alloy. SUMMARY

[0004] In view of the deficiencies of the prior art, the present application provides an environment-friendly cutting fluid and a preparation method thereof. By modifying long-chain dibasic acid with amino acid and then cooperating with amino acid long-chain alcohol ester, a green and environmentally friendly all-synthetic cutting fluid is obtained, which has good lubrication performance and is especially suitable for use in the processing of aluminum alloy.

[0005] The technical purpose of the present application is achieved by the following technical scheme:

[0006] The first aspect of the present application is to provide an environment-friendly cutting fluid, which comprises the following components by weight fraction:

[0007] Long-chain dibasic acid-amino acid 2-20 parts

[0008] Amino acid long-chain alcohol ester 1-20 parts

[0009] Glycerol 1-20 parts

[0010] Sodium metasilicate 0.1-5 parts,

[0011] and water,

[0012] The amount of water added is such that the total mass percentage of the above components in the aqueous solution is 0.5-90wt%;

[0013] The long-chain dibasic acid-amino acid is obtained by connecting two amino acids to the carboxyl groups at both ends of the long-chain dibasic acid; and the amino acid long-chain alcohol ester is an alcohol ester compound formed by the reaction of amino acid and long-chain alcohol.

[0014] As a further preferred, the effective components of the environment-friendly cutting fluid include:

[0015] long-chain diacid-amino acid 7-15 parts

[0016] amino acid long-chain alcohol ester 5-15 parts

[0017] glycerol 7-15 parts

[0018] sodium metasilicate 0.5-2 parts

[0019] Further, the weight ratio of the long-chain diacid-amino acid to the amino acid long-chain alcohol ester is 1-3:1-3, preferably 1-2:1-2.

[0020] Further, the amino acid long-chain alcohol ester is an alcohol ester compound formed by the reaction of an amino acid and a long-chain alcohol, wherein the long-chain alcohol is a C10-C14 n-alkanol, selected from at least one of n-decanol, n-undecanol, n-dodecanol, n-tridecanol and n-tetradecanol, preferably n-undecanol and / or n-dodecanol. The amino acid is selected from at least one of serine, threonine, cysteine and methionine, preferably serine.

[0021] Further, the long-chain diacid-amino acid is obtained by connecting two amino acids to the carboxyl groups at both ends of a long-chain diacid, wherein the long-chain diacid is selected from at least one of undecanedioic acid, dodecanedioic acid, tridecanedioic acid and tetradecanedioic acid, preferably undecanedioic acid or dodecanedioic acid. The amino acid is selected from at least one of proline, phenylalanine, methionine, tryptophan, glutamine, cysteine, tyrosine, lysine, arginine and histidine, preferably at least one of histidine, tryptophan and methionine, most preferably histidine.

[0022] Further, the long-chain diacid-amino acid is preferably dodecanedioic acid-histidine and / or undecanedioic acid-histidine.

[0023] Further, the amino acid long-chain alcohol ester is prepared by the following method: passing anhydrous HCl into a mixed solution of amino acid and long-chain alcohol, heating to reflux, cooling and filtering to obtain amino acid long-chain alcohol ester hydrochloride; dissolving the amino acid long-chain alcohol ester hydrochloride in chloroform, adding solid sodium hydroxide and stirring, then filtering to remove excess sodium hydroxide, and rotary evaporation of the solution to obtain the amino acid long-chain alcohol ester. The heating temperature for reflux is 60-90°C; after adding solid sodium hydroxide, the reaction temperature is maintained at 20-40°C.

[0024] Further, the long-chain dibasic acid-amino acid is prepared by refluxing long-chain dibasic acid and dichloro sulfoxide at 50-120℃ for 2-12h, dissolving the dried solid with NaOH solution, reacting, adding acid, and filtering to obtain the long-chain dibasic acid-amino acid.

[0025] The molar ratio of long-chain dibasic acid to dichloro sulfoxide is 1:1-1:10, preferably 1:3-1:6; the reflux temperature is preferably 70-90℃, and the reflux time is preferably 5-10h. When the amino acid is added, the molar ratio of long-chain dibasic acid to amino acid is 1:0.5-1:4, preferably 1:1-1:3. The dried solid is dissolved with NaOH solution and stirred for 0.5-3h. The concentration of the NaOH solution is 0.1-0.5mol / L. Subsequently, hydrochloric acid, sulfuric acid or nitric acid is added to adjust the pH value of the solution to 1-3.

[0026] The technical purpose of the second aspect of the present application is to provide a preparation method of an environmentally friendly cutting fluid, comprising the following steps:

[0027] The long-chain dibasic acid and dichloro sulfoxide are refluxed at 50-120℃ for 2-12h, the dried solid is dissolved with NaOH solution, and the long-chain dibasic acid-amino acid is obtained by reaction;

[0028] Anhydrous HCl is introduced into the mixed solution of amino acid and long-chain alcohol, heated and refluxed, cooled and filtered to obtain amino acid long-chain alcohol ester hydrochloride; the amino acid long-chain alcohol ester hydrochloride is dissolved in chloroform, solid sodium hydroxide is added and stirred, then excess sodium hydroxide is removed by filtration, and the solution is rotary evaporated to obtain the amino acid long-chain alcohol ester;

[0029] The amino acid long-chain alcohol ester, glycerol and water are mixed, stirred, heated, long-chain dibasic acid-amino acid and sodium metasilicate are added, and stirred until the system is clear and transparent to obtain the cutting fluid.

[0030] Further, when preparing the long-chain dibasic acid-amino acid, the molar ratio of long-chain dibasic acid to dichloro sulfoxide is 1:1-1:10, preferably 1:3-1:6; the reflux temperature is preferably 70-90℃, and the reflux time is preferably 5-10h. When the amino acid is added, the molar ratio of long-chain dibasic acid to amino acid is 1:0.5-1:4, preferably 1:1-1:3. The dried solid is dissolved with NaOH solution and stirred for 0.5-5h. The concentration of the NaOH solution is 0.1-0.5mol / L. Subsequently, hydrochloric acid, sulfuric acid or nitric acid is added to adjust the pH value of the solution to 1-3.

[0031] Further, when preparing the amino acid long-chain alcohol ester, the heating is to 60-90℃; and the reaction temperature is maintained at 20-40℃ after adding solid sodium hydroxide.

[0032] Further, the temperature before adding long-chain dibasic acid-amino acid and sodium metasilicate is raised to 40-60℃.

[0033] The technical purpose of the third aspect of the present application is to provide the application of the above-mentioned environment-friendly cutting fluid, which is used in the aluminum alloy machining process.

[0034] Further, when the cutting fluid is concentrated, the cutting fluid is diluted with water before use, and the total mass concentration of long-chain dibasic acid-amino acid, amino acid long-chain alcohol ester, glycerol and sodium metasilicate is 0.5-8wt%, preferably 2-5wt%.

[0035] Compared with the prior art, the present application has the following advantages:

[0036] (1) The present application uses the combined effect of long-chain dibasic acid-amino acid and amino acid long-chain alcohol ester to make the cutting fluid have strong lubricating performance, which can be used in the machining process of aluminum alloy.

[0037] (2) Long-chain dibasic acid-amino acid and sodium metasilicate have strong aluminum corrosion inhibition, and their combined use can protect aluminum alloy during use.

[0038] (3) Glycerol interacts with amino acid long-chain alcohol ester to effectively improve the extreme pressure performance of the cutting fluid, and glycerol can also help the components of the cutting fluid to disperse better in water.

[0039] (4) The cutting fluid does not contain toxic and harmful substances such as mineral oil, heavy metals and nitrite, and the main components are non-toxic, biocompatible and have strong degradability, so it is a green and environmentally friendly cutting fluid. At the same time, the cutting fluid can be diluted and used according to actual needs by different hardness tap water, which is very suitable for large-scale application.

[0040] Other features and advantages of the present application will be described in detail in the following specific embodiments. Embodiments

[0041] The following non-limiting examples can make those skilled in the art more fully understand the present application, but do not limit the present application in any way. Example 1

[0042] This embodiment discloses an environmentally friendly cutting fluid, the constituent components and the weight percentage of each component are as follows:

[0043] Dodecanedioic acid-histidine: 100g

[0044] Serine dodecanol ester: 90g

[0045] Glycerol: 100 g

[0046] Sodium metasilicate: 10 g

[0047] Deionized water: 700 g

[0048] The cutting fluid is prepared by the following method:

[0049] (1) 230 g of dodecanedioic acid and 469 g of dichloro sulfoxide (molar ratio 1:6) are added to a round-bottom flask and refluxed at 80°C for 12 h. The excess dichloro sulfoxide is removed by rotary evaporation, and the product is dried to obtain a solid. 26.7 g of the above solid and 31 g of histidine (molar ratio of dodecanedioic acid to histidine 1:2) are added to a 1 L 0.2 mol / L NaOH solution and dissolved. After stirring for 1 h, 5 mol / L hydrochloric acid solution is added dropwise until the pH of the solution is 2. Filtration gives dodecanedioic acid-histidine.

[0050] (2) 20 g of serine is dissolved in 500 mL of n-dodecanol, and excess anhydrous HCl is introduced. After heating and refluxing at 80°C for half an hour, it is cooled and filtered to obtain serine dodecanol ester hydrochloride. 50 g of serine dodecanol ester hydrochloride is dissolved in chloroform, 15 g of solid sodium hydroxide is added and stirred, and then excess sodium hydroxide is removed by filtration. The solution is rotary evaporated to obtain serine dodecanol ester.

[0051] (3) According to the above agreed ratio, serine dodecanol ester, glycerol and deionized water are added to the reaction kettle, stirring is started, and the temperature is raised to 50°C. Dodecanedioic acid-histidine and sodium metasilicate are added, and after stirring for 10 min, the system is clear and transparent. After cooling to room temperature, the cutting fluid is obtained.

[0052] The cutting fluid performance test (test standard: Q / SH30310473-2018) is carried out. The prepared cutting fluid is diluted to 5 wt% (mass fraction of other substances except water) solution using tap water. The LY12 aluminum corrosion test maintains qualified time ≥ 48 h, the single piece rust prevention test maintains qualified time ≥ 48 h, and the maximum no-clamping load value is 550 N. Example 2

[0053] This example discloses an environmentally friendly cutting fluid, the constituent components and the weight percentage of each component are as follows:

[0054] Undecanedioic acid-tryptophan: 100 g

[0055] Threonine tridecanol ester: 90 g

[0056] Glycerol: 100 g

[0057] Sodium metasilicate: 10 g

[0058] Deionized water: 700g

[0059] The cutting fluid is prepared by the following method:

[0060] (1) 216g undecanedioic acid and 469g dichloro sulfoxide (molar ratio 1:6) are added to a round-bottom flask and refluxed at 80°C for 12h, the excess dichloro sulfoxide is removed by rotary evaporation, the product is dried to obtain a solid, 25.3g of the above solid and 40.8g of tryptophan (molar ratio of undecanedioic acid to tryptophan 1:2) are added to a 1L 0.2mol / L NaOH solution to dissolve, and stirred for 1h, then 5mol / L hydrochloric acid solution is added dropwise until the solution pH is 2, and filtered to obtain dodecanedioic acid-histidine.

[0061] (2) 20g of threonine is dissolved in 500mL of n-tridecanol, and then excess anhydrous HCl is introduced, heated and refluxed at 80°C for half an hour, then cooled and filtered to obtain threonine tridecanol ester hydrochloride; 50g of threonine tridecanol ester hydrochloride is dissolved in chloroform, 15g of solid sodium hydroxide is added and stirred, then excess sodium hydroxide is removed by filtration, and the solution is rotary evaporated to obtain threonine tridecanol ester.

[0062] (3) According to the above agreed proportion, threonine tridecanol ester, glycerol and deionized water are added to the reaction kettle, stirring is started, the temperature is raised to 50°C, undecanedioic acid-tryptophan and sodium metasilicate are added, the system is clear and transparent after stirring for 10min, and the cutting fluid is obtained after cooling to room temperature.

[0063] The cutting fluid performance test (test standard: Q / SH30310473-2018) is carried out. The prepared cutting fluid is diluted to 5wt% solution with tap water, the LY12 aluminum corrosion test keeps qualified time ≥48h, the single piece rust prevention test keeps qualified time ≥48h, and the maximum no-clamping load value is 510N. Example 3

[0064] This example discloses an environmentally friendly cutting fluid, the constituent components and the weight percentage of each component are as follows:

[0065] Dodecanedioic acid-histidine: 150g

[0066] Serine dodecanol ester: 50g

[0067] Glycerol: 50g

[0068] Sodium metasilicate: 30g

[0069] Deionized water: 720g

[0070] The cutting fluid is prepared by the following method:

[0071] (1) 230 g dodecanedioic acid and 469 g dichloro sulfoxide (molar ratio 1:6) were added to a round bottom flask and refluxed at 80 °C for 12 h, the excess dichloro sulfoxide was removed by rotary evaporation, the product was dried to obtain a solid, 26.7 g of the above solid and 31 g of histidine (molar ratio of dodecanedioic acid to histidine 1:2) were added to a 1 L 0.2 mol / L NaOH solution to dissolve, and stirred for 1 h, then 5 mol / L hydrochloric acid solution was added dropwise until the solution pH was 2, and dodecanedioic acid-histidine was obtained by filtration.

[0072] (2) 20 g of serine was dissolved in 500 mL of n-dodecanol, and excess anhydrous HCl was introduced, heated and refluxed at 80 °C for half an hour, then cooled and filtered to obtain serine dodecanol ester hydrochloride; 50 g of serine dodecanol ester hydrochloride was dissolved in chloroform, 15 g of solid sodium hydroxide was added and stirred, then excess sodium hydroxide was removed by filtration, and the solution was rotary evaporated to obtain serine dodecanol ester.

[0073] (3) According to the above agreed ratio, serine dodecanol ester, glycerol and deionized water were added to the reaction kettle, stirring was started, and the temperature was raised to 50 °C. Dodecanedioic acid-histidine and sodium metasilicate were added, and the system was clear and transparent after stirring for 10 min. After cooling to room temperature, the cutting fluid was obtained.

[0074] The performance of the cutting fluid was tested (test standard: Q / SH30310473-2018). The prepared cutting fluid was diluted to 5 wt% solution with tap water, LY12 aluminum corrosion test was qualified for ≥48 h, single piece rust prevention test was qualified for ≥48 h, and the maximum no-clamping load value was 560 N. Example 4

[0075] This example discloses an environmentally friendly cutting fluid, the constituent components and the weight percentage of each component are as follows:

[0076] Undecanedioic acid-tryptophan: 30 g

[0077] Threonine tridecanol ester: 150 g

[0078] Glycerol: 150 g

[0079] Sodium metasilicate: 40 g

[0080] Deionized water: 630 g

[0081] The cutting fluid was prepared by the following method:

[0082] (1) 216 g of undecanedioic acid and 469 g of dichloro sulfoxide (molar ratio 1:6) were added to a round bottom flask and refluxed at 80 °C for 12 h, the excess dichloro sulfoxide was removed by rotary evaporation, the product was dried to obtain a solid, 25.3 g of the above solid and 40.8 g of tryptophan (molar ratio of undecanedioic acid to tryptophan 1:2) were added to a 1 L 0.2 mol / L NaOH solution to dissolve, and reacted for 1 h under stirring, then 5 mol / L hydrochloric acid solution was added dropwise until the pH value of the solution was 2, and dodecanedioic acid-histidine was obtained by filtration.

[0083] (2) 20 g of threonine was dissolved in 500 mL of n-tridecanol, and then excess anhydrous HCl was introduced, heated and refluxed at 80 °C for half an hour, and then cooled and filtered to obtain threonine tridecanol ester hydrochloride; 50 g of threonine tridecanol ester hydrochloride was dissolved in chloroform, 15 g of solid sodium hydroxide was added and stirred, then excess sodium hydroxide was removed by filtration, and threonine tridecanol ester was obtained by rotary evaporation of the solution.

[0084] (3) According to the above agreed proportion, threonine tridecanol ester, glycerol and deionized water were added to the reaction kettle, stirring was started, the temperature was raised to 50 °C, undecanedioic acid-tryptophan and sodium metasilicate were added, the system was clear and transparent after stirring for 10 min, and the cutting fluid was obtained after cooling to room temperature.

[0085] The performance of the cutting fluid was tested (test standard: Q / SH30310473-2018), the prepared cutting fluid was diluted to 5 wt% solution using tap water, the LY12 aluminum corrosion test maintained qualified time ≥ 48 h, the single piece rust prevention test maintained qualified time ≥ 48 h, and the maximum no-clamping load value was 470 N.

[0086] Comparative Example 1

[0087] The components of the cutting fluid and the weight percentage of each component are as follows:

[0088] Dodecanedioic acid-histidine: 100 g

[0089] Serine: 90 g

[0090] Glycerol: 100 g

[0091] Sodium metasilicate: 10 g

[0092] Deionized water: 700 g

[0093] The preparation of dodecanedioic acid-histidine in the cutting fluid was the same as in Example 1, and the preparation steps of the cutting fluid were the same as in Example 1, except that serine dodecanol ester was replaced by serine.

[0094] Cutting fluid performance test (test standard: Q / SH30310473-2018), tap water is used to dilute the prepared cutting fluid to 5wt% solution, LY12 aluminum corrosion test qualified time ≥ 48h, single piece anti-rust test qualified time ≥ 48h, the maximum no-clamping load value is 200N.

[0095] Comparative example 2

[0096] The components and weight percentages of each component of the cutting fluid are as follows:

[0097] Dodecanedioic acid: 100g

[0098] Serine dodecanol ester: 90g

[0099] Glycerol: 100g

[0100] Sodium metasilicate: 10g

[0101] Deionized water: 700g

[0102] The preparation steps of the cutting fluid are the same as example 1, except that dodecanedioic acid-histidine is replaced by dodecanedioic acid.

[0103] Cutting fluid performance test (test standard: Q / SH30310473-2018), tap water is used to dilute the prepared cutting fluid to 5wt% solution, LY12 aluminum corrosion test qualified time 36h, single piece anti-rust test qualified time ≥ 48h, the maximum no-clamping load value is 500N.

[0104] Comparative example 3

[0105] The components and weight percentages of each component of the cutting fluid are as follows:

[0106] Dodecanedioic acid-histidine: 100g

[0107] Serine: 90g

[0108] Glycerol: 100g

[0109] Deionized water: 710g

[0110] The preparation of dodecanedioic acid-histidine in the cutting fluid is the same as example 1, and the preparation steps of the cutting fluid are the same as example 1, except that sodium metasilicate is not added.

[0111] Cutting fluid performance test (test standard: Q / SH30310473-2018), tap water is used to dilute the prepared cutting fluid to 5wt% solution, LY12 aluminum corrosion test qualified time 36h, single piece anti-rust test qualified time ≥ 48h, the maximum no-clamping load value is 520N.

[0112] Comparative Example 4

[0113] The components of the cutting fluid and the weight percentage of each component are as follows:

[0114] Dodecanedioic acid-histidine: 100 g

[0115] Serine: 90 g

[0116] Sodium metasilicate: 10 g

[0117] Deionized water: 800 g

[0118] The preparation of dodecanedioic acid-histidine in the cutting fluid is the same as in Example 1, and the preparation steps of the cutting fluid are the same as in Example 1, except that no glycerol is added.

[0119] The performance of the cutting fluid is tested (test standard: Q / SH30310473-2018), and the prepared cutting fluid is diluted to a 5wt% solution using tap water. The LY12 aluminum corrosion test maintains a qualified time of ≥48h, the single-piece rust prevention test maintains a qualified time of ≥48h, and the maximum non-galling load value is 450N.

Claims

1. An environmentally friendly cutting fluid, characterized in that, It consists of the following components by weight: 2-20 parts of long-chain dicarboxylic acids-amino acids 1-20 parts of amino acid long-chain alcohol esters Glycerol 1-20 parts Sodium metasilicate 0.1-5 parts, and water, The amount of water added ensures that the total mass percentage of the above components (excluding water) in the aqueous solution is 0.5-90 wt%. The long-chain dicarboxylic acid-amino acid is obtained by attaching two amino acids to the carboxyl groups at both ends of a long-chain dicarboxylic acid. The long-chain dicarboxylic acid is selected from at least one of undecanoic acid, dodecanoic acid, tridecanoic acid, and tetradecanoic acid. The amino acid is selected from at least one of proline, phenylalanine, methionine, tryptophan, glutamine, cysteine, tyrosine, lysine, arginine, and histidine. The long-chain dicarboxylic acid-amino acid is prepared by the following method: the long-chain dicarboxylic acid is refluxed with thionyl chloride at 50-120°C for 2-12 hours. The solid after rotary evaporation and drying is dissolved with amino acids in NaOH solution, reacted, acid is added, and the mixture is filtered to obtain the long-chain dicarboxylic acid-amino acid. The amino acid long-chain alcohol ester is an alcohol ester compound formed by the reaction of amino acids and long-chain alcohols. The long-chain alcohol is selected from at least one of n-decyl alcohol, n-undecyl alcohol, n-dodecanol, n-tetrazol, and n-tetradecyl alcohol. The amino acid is selected from at least one of serine, threonine, cysteine, and methionine. The amino acid long-chain alcohol ester is prepared by the following method: anhydrous HCl is passed into a mixed solution of amino acid and long-chain alcohol, heated under reflux, cooled, and filtered to obtain amino acid long-chain alcohol ester hydrochloride; the amino acid long-chain alcohol ester hydrochloride is dissolved in chloroform, solid sodium hydroxide is added and stirred, then excess sodium hydroxide is removed by filtration, and the solution is rotary evaporated to obtain the amino acid long-chain alcohol ester.

2. The environmentally friendly cutting fluid according to claim 1, characterized in that, The weight ratio of the long-chain dicarboxylic acid-amino acid to the long-chain alcohol ester of the amino acid is 1-3:1-3.

3. The environmentally friendly cutting fluid according to claim 2, characterized in that, The weight ratio of the long-chain dicarboxylic acid-amino acid to the long-chain alcohol ester of the amino acid is 1-2:1-2.

4. The environmentally friendly cutting fluid according to claim 1, characterized in that, The long-chain dicarboxylic acid-amino acid is dodecanoic acid-histidine and / or undecanoic acid-histidine.

5. The environmentally friendly cutting fluid according to claim 1, characterized in that, When preparing long-chain alcohol esters of amino acids, the reflux temperature is 60-90℃; after adding solid sodium hydroxide, the reaction temperature is maintained at 20-40℃.

6. The environmentally friendly cutting fluid according to claim 1, characterized in that, When preparing long-chain dicarboxylic acid-amino acid, the molar ratio of long-chain dicarboxylic acid to thionyl chloride is 1:1-1:10, and when adding amino acids, the molar ratio of long-chain dicarboxylic acid to amino acids is 1:0.5-1:

4.

7. The method for preparing the environmentally friendly cutting fluid according to claim 1, comprising the following steps: Long-chain dicarboxylic acid and thionyl chloride were refluxed at 50-120℃ for 2-12 hours. The solid dried by rotary evaporation was dissolved with amino acids in NaOH solution. After the reaction, acid was added to adjust the pH of the solution to 1-3 to obtain long-chain dicarboxylic acid-amino acid. Anhydrous HCl was passed into a mixed solution of amino acids and long-chain alcohols, heated to reflux, cooled and filtered to obtain amino acid long-chain alcohol ester hydrochloride; the amino acid long-chain alcohol ester hydrochloride was dissolved in chloroform, solid sodium hydroxide was added and stirred, then excess sodium hydroxide was removed by filtration, and the solution was rotary evaporated to obtain the amino acid long-chain alcohol ester. Mix long-chain amino acid esters, glycerol, and water, stir, heat, add long-chain dicarboxylic acid-amino acid and sodium metasilicate, and stir until the system is clear and transparent to obtain the cutting fluid.

8. The preparation method according to claim 7, characterized in that, When preparing long-chain dicarboxylic acid-amino acid, the molar ratio of the long-chain dicarboxylic acid to thionyl chloride is 1:1 to 1:10, and when adding amino acids, the molar ratio of the long-chain dicarboxylic acid to amino acids is 1:0.5 to 1:

4.

9. The preparation method according to claim 7, characterized in that, When preparing long-chain alcohol esters of amino acids, the heating under reflux is to heat to 60-90℃; after adding solid sodium hydroxide, the reaction temperature is maintained at 20-40℃.

10. The application of the environmentally friendly cutting fluid according to claim 1 or the environmentally friendly cutting fluid prepared by the preparation method according to claim 7, wherein the cutting fluid is used in the aluminum alloy machining process.

11. The application according to claim 10, characterized in that, When the cutting fluid is concentrated, it is diluted with water before use until the total mass concentration of long-chain dicarboxylic acid-amino acid, long-chain amino acid ester, glycerol and sodium metasilicate is 0.5-8 wt%.